Yeah, that would be another mundane explanation!

It's lowered my confidence. Though it could have various mundane explanations, the simplest one being that it was taken before he became a vegan, and if so I feel bad about speculating. 

I dug up that conversation, and the point you're referring to is presumably here. The story he tells is: he's trying but failing to be a vegatarian, gets asked by another vegetarian in a social setting whether he is one, says he is, and then never eats meat ever again.

I know I'm contradicting what I just said since it is technically a lie, but honesty this doesn't seem like a big deal to me. ImE you can genuinely lie "without wanting to" in social situations. Someone asks you a question, and some unconscious process in your brain produces an answer within a second before "you" really get to have a say on it. This happened to me several times. And I can understand why it happened here since he was trying to be a vegetarian.

If there is solid evidence that he was lying about being vegan, I'll change my position completely. That'd be a much worse sign than just not being vegan in the first place. (But as you say, [the fact that some people on twitter hinted at] isn't convincing.)

(crossposted from LW) -- I think the [fact that SBF is a vegan and also the way he lives is very strong evidence for the narrative being true. It's the kind of thing many people will dismiss because it's in the "personal life choice" category and perhaps sounds judgy, but the proper Bayesian update here is significant.